U.S. patent number 4,892,619 [Application Number 07/177,472] was granted by the patent office on 1990-01-09 for method of production of fiber containing pulp with different raw materials.
This patent grant is currently assigned to Kamyr AB. Invention is credited to Goran Tistad.
United States Patent |
4,892,619 |
Tistad |
January 9, 1990 |
Method of production of fiber containing pulp with different raw
materials
Abstract
In continuous pulping processes for cellulosic fiberous material
pulp, a changeover from deciduous wood raw material to coniferous
wood raw material without interruption of the production process,
and with a minimum waste of pulp, is provided. The pulp mixture
during changeover, having a consistency of about 8-15% is fed to a
screen in which the pulp is separated into two pulp fractions
depending upon fiber length. A fiber length analyzer is placed in
the pulp stream between a treatment or storage vessel and the
screen, and controls the rejects line from the screen to determine
the amount of pulp passing out the screen rejects conduit. The
screen may be directly in a production line from a continuous
digester, refiner, or like device for producing the pulp, or it may
be connected to a storage vessel to which pulp from a digester or
the like has been fed. The accepts conduit from the screen is
connected to a first vessel while the rejects conduit is connected
to a second vessel, with valves allowing for by-pass of the screen
in feeding the pulp directly into either the first or second vessel
when only a single type of pulp is being produced.
Inventors: |
Tistad; Goran (Karlstad,
SE) |
Assignee: |
Kamyr AB (Karlstad,
SE)
|
Family
ID: |
20368106 |
Appl.
No.: |
07/177,472 |
Filed: |
April 1, 1988 |
Foreign Application Priority Data
|
|
|
|
|
Apr 6, 1987 [SE] |
|
|
87014239 |
|
Current U.S.
Class: |
162/49; 162/141;
162/149; 162/55 |
Current CPC
Class: |
D21D
5/02 (20130101) |
Current International
Class: |
D21D
5/02 (20060101); D21D 5/00 (20060101); D21F
007/06 () |
Field of
Search: |
;162/19,17,82,55,141,142,149,49 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Chin; Peter
Assistant Examiner: Dang; Thi
Attorney, Agent or Firm: Nixon & Vanderhye
Claims
What is claimed is:
1. A method of continuously producing cellulosic fibrous material
pulp during changeover of a pulp production process from a first
raw material for continuously producing a first pulp having a first
property, to a second raw material for continuously producing a
second pulp having a second property different from the first
property, so as to minimize waste of the pulp while maintaining the
integrity of the final pulp produced, comprising the steps of
continuously:
(a) feeding the continuously produced first pulp to a first
location for storage or treatment thereof;
(b) after changeover to the second raw material, feeding the pulp
mixture produced during changeover from the first to the second raw
material, which pulp mixture has pulp with both said first and
second properties, to a screening station;
(c) at the screening station separating the pulp mixture into
separate pulp fractions according to the different first and second
properties of the pulps making up the pulp mixture;
(d) feeding the separated pulp fractions, one fraction comprising
substantially all first pulp and the other fraction substantially
all second pulp, to different locations for storage or treatment of
the first and second pulps; and
(e) once the pulp mixture contains substantially all second pulp,
terminating steps (b) and (c) and feeding the second pulp to a
second location for storage or treatment thereof.
2. A method as recited in claim 1 wherein the different pulp
properties are fiber length, and wherein step (c) is practiced so
as to separate the pulp mixture into pulp fractions by fiber
length.
3. A method as recited in claim 1 comprising the further step (f)
of continuously varying the proportions of first and second pulp
fractions discharged from the screening station in response to the
proportions of first and second pulp in the pulp mixture.
4. A method as recited in claim 3 wherein step (f) is practiced by
sensing the different first and/or second properties of the pulp
mixture prior to its passage to the screening station, and
controlling the discharge flow from the screening station in
response to this sensing.
5. A method as recited in claim 4 wherein the different first and
second properties of the first and second pulps, respectively, are
fiber length, and wherein step (f) is practiced by sensing the
fiber length.
6. A method as recited in claim 4 wherein the pulps and pulp
mixture at all times have a consistency between about 8-15% during
the practice of steps (a) through (f).
7. A method as recited in claim 1 wherein the first raw material is
one of the materials selected from the group consisting of
coniferous wood and deciduous wood, and the second raw material is
the other of the materials selected from the group consisting of
coniferous wood and deciduous wood.
8. A method as recited in claim 1 wherein step (c) is practiced by
placing the screening station directly in a production line from a
production vessel for producing pulp.
9. A method as recited in claim 1 wherein said pulp mixture is
pumped from a storage vessel to the screening station of step
(c).
10. A method as recited in claim 1 wherein step (b) is practiced by
feeding the pulp mixture to a storage vessel, and wherein step (c)
is practiced by withdrawing the pulp mixture from the storage
vessel and then effecting screening thereof.
11. A method as recited in claim 10 wherein the pulps and pulp
mixture at all times have a consistency between about 8-15% during
the practice of steps (a) through (e).
12. A method as recited in claim 10 comprising the further step of
mixing the pulp in the storage vessel so as to provide a completely
homogeneous mixture.
13. A method as recited in claim 1 wherein the pulps and pulp
mixture at all times have a consistency between about 8-15% during
the practice of steps (a) through (e).
14. A method as recited in claim 1 practiced utilizing a treatment
or storage vessel at each location for storage or treatment of
pulp, and a screening station, with valves therebetween, and
wherein the flow or passage of the pulp to the screening station
and the flow or passage of the pulp fractions to the different
locations are controlled by controlling valves.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
During the production of cellulosic fibrous material pulp by
continuous processes, such as the chemical or semi-chemical
digestion of pulp in continuous digesters, or the production of
mechanical pulp in refiners or the like, there are many
circumstances in which it is desirable to change from a first raw
material to a second raw material. For example it is very common to
first be producing pulp from a coniferous wood (e.g. pine wood
chips), and then switch over to the production of pulp from a
deciduous wood (e.g. oak wood chips). If the production is stopped
while changeover occurs so that there is no intermixing of the
coniferous wood pulp and the deciduous wood pulp, the costs to the
mill are substantial, therefore shutdowns are to be avoided.
However during the changeover, a mixture of deciduous and
coniferous pulps will be produced, which pulp mixture is not
suitable for either of the end uses to which the coniferous or
deciduous pulps are normally put. The pulp mixture may adversely
influence the strength or other properties of the deciduous or
coniferous pulps. The quantity of pulp mixture produced can be
considerable in large production units. For example for a
continuous digester that produces 1,000 tons of chemical pulp per
day, the pulp mixture as a result of changeover of raw material can
be about 40 to 50 tons.
According to the present invention it is possible to utilize the
pulp mixture (e.g. the 40 to 50 tons in the example set forth
above) in such a way that it will not be wasted, yet will not have
an adverse affect on the properties of either the coniferous or
deciduous wood pulps (for example). According to the present
invention this is accomplished by terminating the feeding of the
first pulp being produced by the production apparatus, and after
changeover to the second material feeding the pulp mixture produced
during the changeover to a screening station.
At the screening station, in the practice of the invention, the
pulp mixture is separated into pulp fractions having properties
corresponding to the first and second pulps, and the separated pulp
fractions are fed to different locations for storage or treatment.
Once the pulp mixture contains substantially all second pulp (that
is after about 40-50 tons of pulp mixture has passed through, in
the example set forth above), then the steps of feeding the pulp
mixture to a screening station, and screening, are terminated, and
all of the pulp is passed to a second treatment or storage
vessel.
Typically the most significant different property of the first and
second pulps is fiber length. The fiber length of the pulp mixture
may be sensed prior to the screening station, and the proportion of
pulp discharged from the screening station into either the first or
second storage/treatment vessel is controlled in response to the
fiber length analysis.
The screening station may be disposed directly in the discharge
from the continuous treatment vessel (e.g. digester), or
alternatively the pulp mixture can be fed to a storage vessel and
fed from the storage vessel to the screening station. In this
latter case, pumping and screening of the pulp mixture may take
place over a longer period of time than it took to produce the pulp
mixture.
The invention also comprises: A main vessel. At least three
discharge conduits operatively connected to a discharge from the
main vessel. Means for valving the flow of pulp from the main
vessel so that it passes into one of the three discharge conduits.
A first discharge conduit operatively connected to a first vessel.
A second discharge conduit operatively connected to a pulp screen
having an accepts discharge and rejects discharge. A third
discharge conduit operatively connected to a second vessel. An
analyzer for analyzing fiber length operatively connected to the
conduits, and between the screen and the main vessel; and, the
accepts discharge from the screen operatively connected to the
first vessel, and the rejects discharge from the screen operatively
connected to the second vessel.
It is particularly advantageous according to the invention that the
continuous production of pulp, with minimum waste, can take place
without diluting the pulp for conventional screening operations. By
utilizing a screening apparatus that is capable of screening pulp
having a consistency of between about 8-15% (the typical production
consistency), it is possible to avoid the energy waste and the
larger scale equipment that is necessary for diluting and then
rethickening the pulp to screen it at low consistency.
It is the primary object of the present invention to provide an
effective method for continuously producing cellulosic fiberous
material pulp during changeover of a pulp production process from a
first raw material to a second raw material so as to minimize the
waste of the pulp while maintaining the integrity of the final pulp
produced. This and other objects of the invention will become clear
from an inspection of the detailed description of the invention and
from the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 schematically illustrates apparatus that may be utilized in
the practice of the present invention.
DETAILED DESCRIPTION OF THE DRAWING
A main vessel 10 may comprise either a treatment or storage vessel.
For example it can be a continuous digester where a chemical pulp
is being produced, a refiner where mechanical pulp is being
produced, or a storage vessel operatively connected to a digester,
refiner, or other pulp producing facility. A discharge line 11
extends from the main vessel 10, with first, second and third
discharge conduits 12, 13, and 14, respectively, operatively
connected to it. First, second, and third valve means 15, 16, and
17, respectively, are disposed in the conduits 12, 13, and 14. A
control 18 is provided for controlling the valves 15, 16, 17, so
that typically at any one time only one of the valves is open and
the other two are closed.
The discharge conduit 12 is connected to a first vessel 20 for
storage or subsequent treatment of a first pulp, while the third
discharge conduit 14 is operatively connected to a second vessel 22
for storage or subsequent treatment of a second pulp, distinct from
the first pulp. Throughout the main vessel 10, the discharge
conduits 12 through 14, and the vessels 20 through 22, the pulp
typically has a consistency of about 8-15% (e.g. about 10%).
During standard operation when a first raw material 10 is being
used to produce pulp, the valves 16 and 17 are closed while valve
15 is open, with the pulp (first pulp) so produced flowing from the
main vessel 10 directly to the vessel 20. For example during the
production of pulp from deciduous wood, the produced pulp would
flow directly from the main vessel 10 to the vessel 20.
When a second raw material is fed to the pulp production facility,
such as coniferous wood chips, once a changeover of the pulp being
discharged into line 11 (or once the vessel 10 is filled if it is a
storage vessel) occurs, then the valves 15 and 17 are closed and
the valve 16 is open. This pulp mixture, which is a mixture of a
first pulp having the properties of the first raw material (e.g.
deciduous wood), and a second pulp having properties of the second
raw material (e.g. coniferous wood) is fed into conduit 13 and from
there passes to a screening station at which a screen 24 is
provided. The screen 24 is a screen capable of screening pulp at a
consistency of about 8-15%, so that no dilution and rethickening is
necessary. Such a screen may be of the type sold by Kamyr, Inc. of
Glens Falls, N.Y. or Kamyr AB of Karlstad, Sweden under the
trademark "MC", or may be of the type such as shown in U.S. Pat.
Nos. 4,543,181 or 4,680,108. An "accepts" conduit 25 (or multiple
conduits) from the screen 24 leads to the first vessel 20, while a
"rejects" conduit 26 leads from the screen 24 to the vessel 22. The
screen separates the pulp mixture fed into it into two fractions,
one of which is fed to the vessel 20 (the first pulp), while the
other is fed to the vessel 22 (the second pulp).
The first and second pulps of the pulp mixture typically have fiber
length as a distinguishing property thereof. The screen 24 effects
separation depending upon fiber length. Typically, a screen 24
could have a screen drum with slot widths in the range of 0.5-3 mm,
and the slot widths may be provided so as to maximize effective
separation of the pulp mixture into substantially pure first pulp,
and substantially pure second pulp, streams. Also by controlling
the pressure difference over the screen 24, and depending upon the
type of pulp and the temperature, etc., the effectiveness of the
screening operation may be varied.
Typically the power consumption of the screen 24, depending upon
the exact pulp concentration, type, and production rate, would
normally be in the range of about 8-14 kWh/ADMT.
The pulp mixture, over time, will have widely varying proportions
of first and second pulp as the changeover takes place. For example
initially the pulp mixture may have 10% short fibers and 90% long
fibers, while toward the end of the changeover it will have 90%
short fibers and 10% short fibers. This requires that the
proportion of the accepts and rejects from the screen 24 be varied
in proportion to the percentage of long or short fibers in the pulp
mixture. This may be accomplished, according to the invention, by
providing a fiber length analyzer in the conduit 13 just before the
screen 24, and by providing a valve 30--ultimately controlled by
the analyzer 28, through control device 18--in the rejects conduit
26. Alternatively the valve could be provided in one or more
accepts conduits (e.g. U.S. Pat. No. 4,680,108 shows a screening
device with a plurality of accepts conduits) extending from the
screen 24 to the vessel 20.
The analyzer 28 may be any suitable device for sensing fiber length
(or other distinguishing properties of the first and second pulps).
As one example, it may comprise a Kajaani FS-100 fiber length
analysis apparatus manufactured by Valmet Automation of Stockholm,
Sweden. Other commercial fiber length analysis devices also are
available. The analyzer 28 can sense when the valves 15-17 should
be switched, under the control of device 18.
Eventually almost all of the pulp will become second pulp, after
the pulp mixture has been flushed out of the production apparatus.
When that occurs, either by automatic sensing thereof (e.g. with
the analyzer 28), on the basis of the passage of a predetermined
period of time, or otherwise, the control 18 can be actuated so
that the valves 15 and 16 are closed and the valve 17 is open. Then
all of the pulp will pass from the vessel 10 to the vessel 22,
since it is substantially entirely composed of second pulp.
If desired, in order to enhance the efficiency of the screening
operation, a portion of the pulp in the rejects conduit 26 may be
recirculated--as indicated by line 32 in FIG. 1--to a point just
prior to the screen 24.
If the vessel 10 comprises an intermediate storage vessel, instead
of a production vessel (e.g. a continuous digester), then it is
possible to effect the screening over a longer period of time than
the time it takes to produce that pulp. For example if the entire
pulp mixture discharged from the production vessel (e.g. continuous
digester) is fed to a storage vessel (10), and after the mixed pulp
has been exhausted the digester is switched over to a second
storage vessel (e.g. the vessel 22), the pulp may be withdrawn from
the storage vessel (10) by a pump or the like and passed to the
screen 24 in a leisurely manner. This also minimizes the size of
the screen 24 and like equipment that is necessary, yet effects a
result that is advantageous.
Storage vessels utilized in the practice of the invention may be
high consistency storage towers or medium consistency storage
towers. In high consistency towers the pulp is typically stored at
a concentration of 10 to 12% and is discharged by introducing
dilution water to the bottom zone and pumping it out with a pump
capable of handling only low concentration pulp. If a medium
consistency tower is utilized, however, pulp having a consistency
of 10 to 12% is pumped out utilizing a pump capable of pumping such
pulp without dilution (e.g. a pump sold by Kamyr, Inc. of Glens
Falls, N.Y. or Kamyr AB of Karlstad, Sweden under the trademark
"MC").
Thus, according to one aspect of the present invention it is
possible to continuously produce cellulosic fibrous material pulp
during changeover of a pulp production process. For example a
method may comprise the steps of: (a) Continuously feeding a pulp
mixture having a consistency of between about 8-15% to a screening
station. (b) Sensing the proportion of first pulp fiber length with
respect to second pulp fiber length in the pulp mixture prior to
feeding to the screening station. (c) At the screening station,
separating the pulp mixture into separate pulp fractions according
to the different pulp fiber lengths; and, (d) controlling the
discharge of pulp from the screening station depending upon the
results of the sensing in step (b).
As an alternative to the use of an analyzer 28 for controlling
valve 30, if the pulp mixture from the production process is pumped
to a storage tower, it can be mixed together in the tower with a
mixer to provide a homogeneous pulp so that there is approximately
a 50--50 concentration of short and long fibers. That homogeneous
mixture may then be fed directly to a screen 24, with appropriately
dimensioned slots, without the necessity for changing the amount of
pulp passing out the rejects conduit 26, etc.
While the invention has been herein shown and described in what is
presently conceived to be a practical and preferred embodiment
thereof, it will be apparent to those of ordinary skill in the art
that many modifications may be made thereof within the scope of the
invention, which scope is to be accorded the broadest
interpretation of the appended claims so as to encompass all
equivalent methods and structures.
* * * * *